1. KThumath Saint Paul's 12/3/02
Topic 14 Fertilisers
kathryn thumath
30/12/2018
KThumath Saint Paul's 12/3/02

2. KThumath Saint Paul's 12/3/02
What are Fertilisers?
Fertilisers are substances we add to the soil to replace essential elements that plants need to grow.
They can be natural or synthetic.
We need fertilisers because we are exhausting the soils natural nutrients due to increasing demands for foods.
This is because the worlds population is increasing.
30/12/2018
KThumath Saint Paul's 12/3/02

3. KThumath Saint Paul's 12/3/02
Natural Fertilisers
Natural fertilisers can be split into two groups: Compost and Manure
Compost – is made from rotting plants.
Manure – is animal waste
When both plants and animals die they rot releasing ammonium compounds into the ground.
Bacteria in the soil convert these to nitrates which can then dissolve and be taken in by plants. This is part of the “Nitrogen Cycle”
30/12/2018
KThumath Saint Paul's 12/3/02

4. Synthetic Fertilisers
These are man made and contain the three essential plant elements:
Nitrogen
Potassium
Phosphorous
Known collectively as NPK
Each synthetic fertiliser will contain a different amount of each element.
30/12/2018
KThumath Saint Paul's 12/3/02

5. KThumath Saint Paul's 12/3/02
Leguminous Plants
These are plants which contain bacteria in special root nodules.
The bacteria are able to use Nitrogen from the Air to make Nitrates.
This is called Nitrogen Fixation
Examples of legumes – clover, beans or peas.
30/12/2018
KThumath Saint Paul's 12/3/02

6. What makes a good Fertiliser?
They must contain essential elements (NPK)
They must be soluble – to enable absorption by plant roots.
However if they are too soluble they may be washed away with rain!
They must be easy to spread.
Urea is exception – only slightly soluble but has very high Nitrogen content.
30/12/2018
KThumath Saint Paul's 12/3/02

7. Making Synthetic Fertilisers
They are salts made in neutralisation reactions.
Example
Ammonia + Nitric Acid= Ammonium nitrate
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KThumath Saint Paul's 12/3/02

8. Calculating % mass of an element in a compound.
Step 1 – Calculate correct formula of compound. Calculate 1 mole.
Step 2 - Count the number of atoms of the particular element in the compound. Add up the total mass of that element in the compound.
Step 3 -Use the equation –
% mass of element= Mass of element in compound/ total mass of compound. X 100
30/12/2018
KThumath Saint Paul's 12/3/02

9. KThumath Saint Paul's 12/3/02
Worked Example
Calculate the % mass of Nitrogen in Ammonium nitrate
Step 1 – Formula = NH4NO Mole = ( 2xN) + (3xO) + (4xH) =80g
Step 2 – No. of N in compound =2( 2x14 = 28)
Step3 - Mass of N in compound/Total Mass of compound x 100
Answer – 28/80 x 100 = 35%
30/12/2018
KThumath Saint Paul's 12/3/02